Trackball fixes

So I've somewhat re-factored how I handled both the screen->element coordinates and the spherical (vs oblong) trackball issues.  

Instead of changing getMouseProjectionOnBall, I changed the "screen" variable and the updater in handleResize.  This has the side effect that it also affects the pan & zoom elements, but they seem to work fine.

Finally, I've also put in the "noRoll" option which toggles the external roll "ring"